∫[sin^2(x)]*[cos^2(x)]dx
=∫（sinxcosx）^2dx
=∫（sin2x/2）^2dx
=1/4∫(sin2x)^2dx
=1/8∫(1-cos4x)dx
=x/8-1/32∫cos4xd4x
=x/8-1/32sin4x+C